It is often necessary or desirable to obtain a measurement of the intensity of light within a particular spectral region, in a particular location. This need arises in a variety of contexts.
For example, photosynthetic active radiation (PAR) designates the spectral range of solar light from 400 to 700 nanometers that photosynthetic organisms use during photosynthesis. While nearly all plants absorb radiation in the PAR range, the required light intensity varies significantly from plant to plant. Each plant demonstrates its best performance when subject to its optimal light intensity. Optimal light intensities vary from full sunlight to complete shade, depending on the species. Full sunlight, which is optimal for a plant like maize (Zea mays L.) would be lethal to an understory plant like clover (Trifolum sp.). For plant owners, horticulturalists and botanists, for example, matching the light source to a plant's optimal lighting condition is essential to the plant's livelihood.
A similar measurement may be necessary underwater, to determine, for example, the optimal light conditions for underwater plant and animal life.
Likewise, ultraviolet (UV) radiation lies in the spectral range of solar light from approximately 100 to 400 nanometers. UV radiation most notably causes sunburn, however, it is also used extensively in both curing systems and sterilization systems. As such, the detection of UV light is useful in a variety of applications. A person visiting the beach may wish to detect the intensity of UV light for the purpose of determining the sun protection factor (SPF) necessary to prevent sunburn. A scientific researcher may need to detect the intensity of a UV light bulb in order to determine whether a particular bulb is effective for germicidal irradiation. Similarly, a dentist may wish to detect whether the intensity of light produced by a UV bulb in a light curing system is effective for curing various composites and materials used in dentistry.
Existing devices, commonly referred to as radiometers or photometers, vary significantly in functionality. For example, many existing devices quantify the accumulation of light over time. Because this type of device does not provide an instantaneous reading it is impractical in many situations. It is untimely for a casual plant owner wishing to position a new plant in optimal lighting conditions. Similarly, a device that measures light accumulation over an extended period of time is untimely for an individual wishing to apply sunscreen upon arrival at the beach. Further, existing devices are either battery-powered or require an external power source. Use of batteries has major disadvantages including cost, inconvenience and environmental toxicity. And providing an external power source is difficult in many situations, including where the device is intended for use outdoors. As such, the power source requirement is often prohibitive.
In view of the foregoing, there is a need to provide a self-contained, battery-free light intensity measurement device. The device should be small and flexible such that it is useful in a variety of light intensity measurement applications. It is further desirable that such a device be inexpensive to manufacture such that the device can be offered in a disposable form. The present invention addresses one or more of these needs.